Interengaging rotor displacement machine

ABSTRACT

A rotary displacement machine provided with a casing having pipe connections for the suction and discharge of the working fluid. The discharge pipe connection communicates with discharge ports made on each face surface of the casing. Installed rotatably inside the casing is a driving straight-toothed rotor and a driven straight-toothed rotor. The profiles of the teeth of the driving and driven rotors are selected so that on rotating, these teeth roll over one another. The driving rotor rotates the driven rotor via a train of two meshing gears. One of the meshing gears is installed on the shaft of the driving rotor and the other gear on the shaft of the driven rotor. Apart from transmitting rotation, the meshing gears ensure a guaranteed clearance between the rotor teeth which is required for a reliable performance of the machine. The cylindrical surface of the driving straighttoothed rotor is provided with lobes which are located, each between the rotor teeth. Each tooth of the driven rotor has a depression on the external cylindrical surface for equalizing the pressure between the cavities of the driven and driving rotors during compression of the working fluid. The cavity of the driven rotor is formed by a space between its teeth and the internal surface of the casing. The cavity of the driving rotor is formed by the space between its teeth and the internal surface of the casing. The depression on the cylindrical surface on the driven rotor tooth is limited at the front edge of the tooth, in the direction of rotation of the driven rotor, by the body of the tooth and at both faces of the tooth also by the body of the tooth. The dimensions of the depression correspond to the dimensions of the lobe on the cylindrical surface of the driving rotor so that during rotation of both rotors, the lobe covers the depression and separates the zone of equalized pressure from the suction zone.

United States Patent [191 Abaidullin et al.

[ July 15, 1975 INTERENGAGING ROTOR DISPLACEMENT MACHINE [22] Filed: Apr. 22, 1974 [2|] Appl. No.: 463,097

[52] US. Cl. 418/191 [5!] Int. F011 1/08; F04c 17/04 [58] Field of Search 418/9, l0, l89l91 [5 6] References Cited UNITED STATES PATENTS 899,l48 /1908 Westrich .r 418/l9l 2,464,48l 3/1949 Berry 4l8/9 2,786,332 3/l957 Tavcrnicrs 4l8/l9l 3.453.992 7/l969 Graham 4l8/l9l 3,6l2,735 IO/l97l Graham 4l8/l9l Primary Examiner-John J. Vrablik Attorney, Agent, or Firm-Holman & Stern [57] ABSTRACT A rotary displacement machine provided with a casing having pipe connections for the suction and discharge of the working fluid. The discharge pipe connection communicates with discharge ports made on each face surface of the casing. Installed rotatably inside the easing is a driving straight-toothed rotor and a driven straight-toothed rotor. The profiles of the teeth of the driving and driven rotors are selected so that on rotating. these teeth roll over one another. The driving rotor rotates the driven rotor via a train of two meshing gears. One of the meshing gears is installed on the shaft of the driving rotor and the other gear on the shaft of the driven rotor. Apart from transmitting rotation, the meshing gears ensure a guaranteed clearance between the rotor teeth which is required for a reliable performance of the machine. The cylindrical surface of the driving straight-toothed rotor is provided with lobes which are located, each between the rotor teeth. Each tooth of the driven rotor has a depression on the external cylindrical surface for equalizing the pressure between the cavities of the driven and driving rotors during compression of the working fluid. The cavity of the driven rotor is formed by a space between its teeth and the internal surface of the casing. The cavity of the driving rotor is formed by the space between its teeth and the internal surface of the casing. The depression on the cylindrical surface on the driven rotor tooth is limited at the front edge of the tooth, in the direction of rotation of the driven rotor, by the body ofthe tooth and at both faces of the tooth also by the body of the tooth. The dimensions of the depression correspond to the dimensions of the lobe on the cylindrical surface of the driving rotor so that during rotation of both rotors, the lobe covers the depression and separates the zone of equalized pressure from the suction zone.

3 Claims, 9 Drawing Figures INTERENGAGING ROTOR DISPLACEMENT MACHINE BACKGROUND OF THE INVENTION The present invention relates to rotary displacement machines in which the working fluid is compressed or expanded due to changes in the working volume and more specifically to rotary displacement machines.

The present invention can be used most successfully in compressors intended to power pneumatic tools and supercharge the internal combustion engines; also in rotary engines and gas-expansion machines used, for the production of liquiefied gases.

PRIOR ART Known in the art is a rotary displacement machine, for example, a compressor with partial internal compression (A. G. Golovintsev e.a. Rotary Compressors," p. 215, Mashinostryenie," Moscow, 1964, USSR).

The known rotary machine comprises a casing with suction and discharge pipe connections. Installed rotatably in the casing is a driving straight-toothed rotor and a driven straight-toothed rotor. The tooth profiles of the driven and driving rotors are selected such that the teeth of the rotating rotors roll over one another. The driving rotor rotates the driven rotor via a gear train consisting of two meshing gears. One of said gears is installed on the shaft of the driving rotor and the other on the shaft of the driven rotor. Apart from transmitting rotation, the gears ensure a guaranteed clearance between the rotor teeth which is required for a reliable operation of the compressor.

During rotation of the rotors, the working fluid enters the cavities of both rotors through the suction pipe connection. The cavity of the driving rotor is formed by a space between the teeth and the internal surface of the casing. The cavity of the driven rotor is likewise formed by a space between the teeth and the internal surface of the casing. During further rotation of the rotors, the tooth of the driving rotor disconnects the cavity of the driving rotor from the suction pipe connection and the tooth of the driven rotor disconnects the cavity of the driven rotor from the suction pipe connection. Further turning of the rotor reduces the volume of the cavity of the driving rotor because the tooth of the driven rotor enters this cavity. This raises pressure in the cavity of the driving rotor. The compressed fluid is pushed out into the discharge pipe connection through the cavity of the driven rotor.

The known rotary machine is simple to manufacture, reliable, and has a long service life due to a complete absence of the axial forces which do not arise because of the equal pressure of the working fluid applied to both faces of the rotors.

However, in spite of the above-mentioned advantages. these machines are not in widespread use. This should be attributed to the fact that there is no internal compression of the working fluid in the cavity of the driven rotor. The working fluid is carried in the cavity of the driven rotor from the suction side to the discharge side without being compressed. inasmuch as the amount of gas transferred from the suction to the discharge side without internal compression constitutes a fairly large proportion of the total compressor output 16-22 percent). the efficiency of such machines, par ticularly at high pressure rise ratios, is low.

This disadvantage has been partly countered in another rotary displacement machine, e.g. in the air blower disclosed in Patent No. 992,226, Great Britain. This machine has a suction pipe connection and a discharge pipe connection. The discharge pipe connection communicates with the discharge ports on each face surface of the casing. Installed rotatably in the casing is a driving straight-toothed rotor and a driven straighttoothed rotor. The tooth profiles of the driving and driven rotors are selected so that the teeth of the rotating rotors roll over one another. The driving rotor rotates the driven rotor via a gear train consisting of two meshing gears. One of these gears is installed on the shaft of the driving rotor and the other on the shaft of the driven rotor. Apart from transmitting rotation, the gears ensure a guaranteed clearance between the rotor teeth which is required for a reliable operation of the compressor.

The cylindrical surface of the driving straighttoothed rotor has lobes, with each lobe being positioned between the rotor teeth. The cylindrical surface of each tooth of the driven straight-toothed rotor has a depression for equalizing the pressure between the cavity of the driven rotor and that of the driving rotor in the process of compression of the working fluid, the depression being limited by the body of the tooth at the front edge of the tooth, in the direction of rotation of the driven rotor. The cavity of the driven rotor is formed by a space between the teeth and the internal surface of the casing. The cavity of the driving rotor is formed by a space between the teeth and the internal surface of the casing. The dimensions ofthe lobe on the cylindrical surface of the driving rotor correspond to the dimensions of the depression on the external cylindrical surface of the driven rotor tooth so that during rotation of the driving and driven rotors, the lobe covers the depression and separates the zone of equalized pressure from the suction zone.

During rotation of the rotors. the working fluid flows through the suction pipe connection into the cavities of the driving and driven rotors. During further rotation of the rotors, the tooth of the driving rotor disconnects the cavity of the driving rotor from the suction pipe connection and the tooth of the driven rotor disconnects the cavity of the driven rotor from the suction pipe connection. Further rotation of the rotors reduces the volume of the cavity of the driving rotor because the tooth of the driven rotor enters this cavity and thus leads to an increase of pressure in the cavity of the driving rotor. Still further rotation of the rotors brings the front edge of the tooth from under the recess in the casing. The cavity of the driven rotor is then placed in communication with the cavity of the driving rotor through the depression on the cylindrical surface of the driven rotor tooth. Further compression of the working fluid occurs simultaneously in both cavities after which the compressed fluid is pushed out through the discharge ports into the discharge pipe connection.

The known rotary displacement machine has a low efficiency at medium and high pressure rise ratios. This can be explained by the fact that the height of the depression on the cylindrical surface of the driven rotor tooth is interrelated with the size of the discharge port. At ordinary pressure rise ratios in the compressor (2 4), the satisfactory area of the discharge port is obtained by increasing the radius of the internal cylindrical surface of the depression on the driven rotor teeth.

However, this results in a small cross-sectional area of the depression which provide communication between the cavity of the driven rotor and that of the driving rotor; This small area proves to be inadequate for equalizing pressure in the cavities in view of the high hydraulic resistances to the flow of the working fluid from the cavity of the driving rotor into the cavity of the driven rotor. This reduces the efficiency of the machine.

A reduction of the radius of the internal cylindrical surface of the depression on the teeth of the driven rotor results in a sharp reduction of the area of the discharge port which can be made only on the face surface of the compressor casing below the internal cylindrical surface of the depression. A decrease in the area of the discharge port increases sharply the hydraulic losses for pushing the compressed working fluid through said port which reduces considerably the efficiency of the machine.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to increase the efficiency of a rotary displacement machine at medium and high pressure rise ratios.

In accordance with this and other objects, the present invention consists in providing a rotary displacement machine with suction and discharge pipe connections located in a casing which accommodates a rotatably installed driving straight-toothed rotor whose cylindrical surface has lobes with each lobe between the rotor teeth and a driven straight-toothed rotor which is rotated by the driving rotor via a gear train, each tooth of the driven rotor being provided on the external cylindrical surface with a depression intended to equalize the pressure between the cavity of the driven rotor formed by the space between the teeth and the internal surface of the casing and the cavity of the driving rotor formed by the space between its teeth and the internal surface of the casing in the process of compression of the working fluid and limited by the body of the tooth at the front edge of the tooth, in the direction of rotation of the driven rotor, the dimensions of the lobe on the cylindrical surface of the driving rotor corresponding to the dimensions of the depression on the external cylindrical surface of the driven rotor tooth so that during rotation of the rotors, the lobe covers the depression and separates the zone of equalized pressure from the suction zone wherein, according to the invention, the depression on the cylindrical surface of the driven rotor tooth is limited by the body of the tooth at both tooth faces.

The rotary displacement machine realized according to the invention has a high efficiency at medium and high pressure rise ratios. This is obtained by making the discharge port of any required height within the limits of the tooth height because the depression is separated from the casing by the body of the tooth.

An increase in the area of the discharge port brings about a sharp decrease in the hydraulic losses for pushing the compressed working fluid into the discharge port which raises considerably the efficiency of the machine.

Besides, the depression on the cylindrical surface of the driven rotor tooth can have any depth within the limits of the tooth height. Thus, it becomes possible to make such an area through the depression which ensures a low velocity, not higher than 20-30 m/s, of the working fluid flowing from the cavity of the driving rotor into the cavity of the driven rotor. Calculations of the pressure losses involved in the flow of the working fluid from one cavity to the other shows that at these velocities, these losses amount to a mere 0.02-0.03 kg/cm".

Thus, the pressures of the working fluid in the cavities of the driven and driving rotors become in fact completely equalized which ensures a high efficiency of the rotary displacement machine.

It is practicable that the front side of the depression on the cylindrical surface of the driven rotor, in the direction of its rotation, should be described by an arc whose outer lies on the pitch circle of the driven rotor and whose radius is equal to the difference between the radii of the driven rotor pitch circle and the inside circle of the depression, that the front side of the lobe, in the direction of driving rotor rotation, should be described by an arc whose center lies on the driving rotor pitch circle and whose radius is equal to the difference between the radii of the outside circle of the lobe and of the pitch circle and that the back side of the lobe should have the form of a shortened epicycloid constituted by the point of intersection of the inside diameter of the depression on the cylindrical surface of the tooth with the space between the teeth of the driven rotor when the pitch circle of the driven rotor rolls over the pitch circle of the driving rotor without slipping.

Such a design of the front side of the depression on the driven rotor and of the front side of the lobe on the driving rotor prevents the formation of a crescent gap. In the crescent gap, the working fluid cannot escape either to the suction side or the discharge side and is compressed in said gap to very high undesirable pressures. This compression requires additional energy of the motor which rotates the driving rotor and thus reduces the efficiency of the rotary displacement machine. The crescent gap is not formed in the rotary displacement machineaccording to the invention because at the moment when the point of intersection of the outside circle of the lobe with the arc whose center lies on the rolling circle of the driving rotor is located on a line connecting the rotor axes of rotation so that the front side of the lobe contacts the front side of the depression along the entire are.

It is practicable that the front side of the depression on the cylindrical surface of the driven rotor tooth, in the direction of rotation of the driven rotor, should be described by an arc whose center lies outside the rolling circle of the driven rotor and the front side of the lobe, in the direction of rotation of the driving rotor, should follow a rolling curve which satisfies the fundamental gearing theorem and ensures a continuous contact between said front side of the depression and said front side of the lobe and that the back side of the lobe should follow a shortened epicycloid formed by the point of intersection of the inside diameter of the depression on the cylindrical surface of the tooth with the space between the teeth of the driven rotor during rolling of the driven rotor pitch circle without slipping over the pitch circle of the driving rotor.

In such a design of the front side of the depression on the driven rotor and of the front side of the lobe on the driving rotor, there is no crescent gap either so that it does not reduce the efficiency of the machine. When the front side of the depression on the cylindrical surface of the driven rotor tooth is described by an arc whose center lies outside the rolling circle of the driven rotor, this simplifies the manufacture of an integral driven rotor.

Other objects and advantages of the invention will now be described in detail by way of example with reference to the drawings. in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinal section of the rotary displacement machine according to the invention;

FIG. 2 is a section taken along line II-II in FIG. 1 the view looking in the direction of the arrows;

FIG. 3 is perspective view of the driving and driven rotors according to the invention;

FIG. 4 is a section taken along line lV-IV in FIG. 2 the view looking in the direction of the arrows and illustrating the driven and driving rotors at the beginning of compression of the working fluid in the rotor cavities;

FIG. 5 is a section taken along line V-V in FIG. 2 the view looking in the direction of the arrows and illustrating the driven and driving rotors at the end of compression of the working fluid and beginning of discharge;

FIG. 6 shows the position of the rotors according to the invention at the end of the working fluid discharge;

FIG. 7 shows the position of the rotors according to the invention at the moment of contact between the front side of the lobe on the driving rotor and the front side of the depression on the driven rotor;

FIG. 8 shows the position of the rotors according to the invention at the moment when the point obtained by the intersection of the inside diameter of the depression on the cylindrical surface of the tooth with the space between the teeth of the driven rotor contacts the back side of the lobe on the driving rotor; and

FIG. 9 is a cross section of another form of the rotary displacement machine according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The rotary displacement machine, e.g. a compressor. comprises a casing (FIG. 1) having a suction pipe connection 2 and a discharge pipe connection 3. The discharge pipe connection 3 communicates with two discharge ports 4, each being provided on the face surface of the casing 1. Installed rotatably inside the casing on bearings 5 are a driving straight-toothed rotor 6 (FIG. 2) and a driven straight-toothed rotor 7. The driving rotor 6 rotates the driven rotor 7 via a gear train consisting of two connecting or meshing gears 8 and 9. The gear 8 is mounted on a shaft 10 of the driving rotor 6 while the gear 9 is mounted on a shaft 11 of the driven rotor 7. The gears 8 and 9 ensure a guaranteed clearance between the teeth of the rotors 6 and 7 which is required for a reliable operation of the compressor. The driving straight-toothed rotor 6 has lobes 13 on its cylindrical surface 12 (FIG. 3). With each lobe being located between teeth 14 of the rotor 6. Each tooth 15 of the driven rotor 7 has a depression 17 on its external cylindrical surface 16, With said depression being limited by the body of the tooth 15 at its front edge. in the direction of rotation of the driven rotor 7, shown by arrow A, and at both faces of the tooth 15.

The depression 17 equalizes pressure between a cavity 18 (FIG. 4) of the driven rotor 7 and a cavity 19 of the driving rotor 6 in the course of compression of the working fluid. The cavity 18 is formed by a space 20 between the teeth 15 and an internal surface 21 of the casing l. The cavity 19 is formed by a space 22 between the teeth 14 and the internal surface of the easing 1. The dimensions of the lobe 13 on the cylindrical surface 12 (FIG. 3) of the driven rotor 6 correspond to the dimensions of the depression 17 on the external cylindrical surface 16 of the tooth 15 of the driven rotor 7 so that, during rotation of the driving and driven rotors 6 and 7, the lobe 13 covers the depression 17 and separates the zone of equalized pressure from the suction zone. The profile of the teeth 14 of the driving rotor 6 and the teeth 15 of the driven rotor 7 is selected so as to avoid both the transverse leakage" and the locked volume" of the compressor which raises considerably its efficiency. The term transverse leakage should be understood as the flow of the working fluid from the space 20 (FIG. 4) with the inserted tooth 14 of the driving rotor 6 through the clearance formed by the front edge of the tooth 15, in the direction of rotation of the driven rotor 7 shown by arrow A, and the back side of the tooth 14 in the direction of rotation of driving rotor shown by arrow B.

The term locked volume should be understood as the volume of the working fluid enclosed between the space 20 and the inserted tooth l4 and having no escape towards the discharge side. The absence of transverse leakage and locked volumes is obtained by the use of asymmetrical profiles in which the back side of the tooth 14, in the direction of arrow B showing the rotation of the driving rotor 6, follows an epicycloid while the front side is outlined by any curves with which the ratio of the width b of this part of the tooth 14 counted over a tangent line to the pitch circle of the driving rotor 6 to its height it exceeds or equals a unity. In this case, the space 20 between the teeth 15 of the driven rotor 7 follows the corresponding rolling curves which satisfy the requirements of the fundamental gearing theorem and the condition of continuous contact.

The front side 23 of the depression 17 in the direction of rotation of the driven rotor 7 shown by arrow A is described by an arc whose centre lies on the pitch circle of radius r and whose radius is equal to the difference between the radiuses of the pitch circle n of the driven rotor 7 and of the inside circle of the depression 17.

A front side 24 of the lobe 13, in the direction of rotation of the driving rotor shown by arrow B, is described by an arc whose center lies on a pitch circle r of the driving rotor 6 and whose radius is equal to the difference between the radii of the outside circle of the lobe 13 and of the pitch circle r, of the driving rotor 6.

A back side 25 of the lobe 13 is described by a shortened epicycloid which is formed by a point 26 of intersection of the inside diameter of the depression 17 on the tooth 15 with the space 20 between the teeth 15 of the driven rotor 7 when a pitch circle r, of the driven rotor 7 rolls without slipping over the pitch circle r of the driving rotor 6.

The compressor operates as follows:

The shaft 10 (FIG. 2) of the driving rotor 6 is rotated by a motor (not shown in the drawing). Rotation of the driving rotor is transmitted by the gear 8 to the gear 9 located on the shaft 11 of the driven rotor 7. During rotation of the rotors 6 and 7, the working fluid flows through the suction pipe connection 2 (FIG. 4) into the space 20 of the driven rotor 7 and the space 22 of the driving rotor 6.

When the rotors 6 and 7 occupy the position shown in FIG. 4, the spaces 20 and 22 are separated from the suction pipe connection 2 which corresponds to the beginning of compression of the working fluid. In the course of further rotation of the rotors 6 and 7, the tooth 15 of the driven rotor 7 enters the cavity 19 of the driving rotor 6 and the working fluid is compressed in said cavity. The back side of the tooth 14, in the direction of rotation of the driving rotor 6 shown by arrow B, described by an epicycloid prevents the transverse leakage in the compressor because the teeth 14 and 15 come in contact immediately after the top of the tooth 14 of the driving rotor 6 and the front edge of the tooth 15, in the direction of rotation of the driven rotor 7 shown by arrow A, come from under the internal surface 21 near a ridge 27. The line of contact separates the space 20 with the inserted tooth 14 from the cavity 19 with a different pressure. During further rotation of the rotors 6 and 7, the front edge of the tooth 15 of the driven rotor 7 passes the ridge 27 of the bore in the easing 1. Then, the cavity 18 of the driven rotor 7 will come in communication with the cavity 19 (FIG. 4) of the driving rotor 6 through the depression 17 on the cylindrical surface 16 (FIG. 3) of the tooth 15. Further compression of the working fluid takes place concurrently in both cavities l8 and 19.

At the moment (shown in FIG. 5) the cavity 18 of the driven rotor 7 approaches the edges 28 of the discharge ports 4, the compression of the working fluid is completed and the process of discharge begins. By changing the position of the edges 28 of the discharge ports 4, it is possible to change the geometrical compression ratio of the compressor. The compressed fluid is forced through the discharge ports 4 into the discharge pipe connection 3.

The process of discharge ends at the moment (shown in FIG. 6) when the cavity 18 of the driven rotor 7 becomes separated from the discharge pipe connection 3 at edges 29 of the discharge ports 4. In this case, according to the gearing theorem, only in the profiles of the teeth 14 and 15 of the rotors 6 and 7 with a ratio h/h 1 the point of contact between the teeth 14 and 15 moves during rotation of the rotors 6 and 7 from the lower part of the tooth 14 of the driving rotor 6 to the periphery. The front side of the tooth 14, in the direction of rotation of the driving rotor 6 shown by arrown B, comes out of contact with the front side of the tooth 15, in the direction of rotation of the driven rotor 7 shown by arrow A, when the top of the tooth 14 passes the line connecting the rotation axes of the rotors 6 and 7. By this moment. the compressed working fluid is completely forced out of the cavity 18 by the tooth 14 of the driving rotor into the discharge ports 4. This accounts for the absence of the locked volumes in the compressor.

In the process of discharge of the working fluid illustrated in H0. 7, the lobe 13 on the driving rotor 6 enters the depression on the driven rotor 7 without forming a locked volume in which the gas could be compressed to a considerable pressure thus causing additional power losses of the motor (not shown in the Figare) and irregular performance of the compressor. At this moment the, point 30 of intersection between the outside circle of the lobe 13 with the arc whose center lies on the rolling circle r, of the driving rotor 6 is located on the line connecting the axes of rotation of the rotors 6 and 7 so that the front side 24 of the lobe l3 contacts the front side 23 of the depression 17 along the entire arc. At the following moment of time illustrated in H6. 8, the back side 25 of the lobe 13 on the driving rotor 6 described by a shortened epicycloid is in constant contact with the point 26 of intersection between the inside diameter of the depression 17 on the tooth 15 of the driven rotor 7 with the space 20 between the teeth 15 of the driven rotor 7. Only this profile of the back side 25 of the lobe 13 makes it possible to avoid formation of a gap between the lobe l3 and the depression 17 through which the compressed working fluid leaks into the suction zone thus reducing the output and efficiency of the compressor. It is possible to make additional discharge ports 31 (FIG. 1) on the cylindrical surface on the casing l in the zone of the body of the tooth 15 of the driven rotor 7, with said body limiting the depression 17 at both faces of the tooth 15 of the driven rotor 7. This will reduce hydraulic losses in the discharge ports 4 and 31 and increase the efficiency of the compressor.

ln another embodiment of the compressor according to the invention a front side 32 (H6. 9) of the depression 17 on the cylindrical surface 16 of the tooth 15 of the driven rotor 7, in the direction of rotation of the driven rotor 7 shown by arrow A, is described by an arc r whose center lies outside the pitch circle r, of the driven rotor 7. A front side 33, in the direction of rotation of the driving rotor 6 shown by arrow B, of the lobe 13 located between the teeth 14 of the driving rotor 6 is described by a rolling curve which satisfies the fundamental gearing theorem and the requirement of continuous contact between the front side 32 of the depression 17 and the front side 33 of the lobe 13. Such an outline of the front side 32 of the depression 17 of the driven rotor 7 and of the front side 33 of the lobe 13 of the driving rotor 6 also makes it possible to avoid a locked volume which reduces the compressor efficiency. If the front side 32 of the depression 17 of the driven rotor 7 is described by an are r, whose center lies outside the pitch circle r, of the driven rotor 7, this simplifies the manufacture of integral driven rotor 7. In other respects, the compressor is similar to the one described above and operates on the same principle.

[f the rotary displacement machine is used in the capacity of, say, a gas-expansion machine, the compressed working fluid is delivered into the pipe connection 3, expands in the cavity 18 of the driven rotor 7 and in the cavity 19 of the driving rotor 6 and enters the pipe connection 2. ln this case, rotation of the driving rotor 6 and driven rotor 7 is reversed.

We claim:

1. A rotary displacement machine comprising: a casing having an internal surface; a pipe connection located on said casing and serving for sucking in the working fluid; a pipe connection located on said casing and serving for discharging the working fluid; a straight-toothed driving rotor installed rotatably in said casing; said driving rotor having a cylindrical surface; lobes located on said cylindrical surface of said rotor, each lobe being positioned between said straight teeth of said rotor; at straight-toothed driven rotor installed inside said casing; a gear train consisting of two meshing gears for transmitting rotation from said driving rotor to said driven rotor and for ensuring a guaranteed clearance between said teeth of said driven and driving rotors; a shaft for said driving rotor which carries one of said meshing gears; a shaft for said driven rotor which carries the other of said meshing gears; an external cylindrical surface for each tooth of said driven rotor; spaces between said teeth of said driving rotor and driven rotor; a cavity for said driven rotor formed by said space between said teeth of said driven rotor and the internal surface of said casing; a cavity for said driving rotor formed by said space between said teeth of said driving rotor and the internal surface of said casing; a depression serving to equalize pressure between said cavity of said driven rotor and said cavity of said driving rotor during compression of the working medium, said depression being located on said cylindrical surface of each tooth of said driven rotor and limited by the body of said tooth at the front edge of said driven rotor tooth, in the direction of rotation of said driven rotor, and by the body of the same tooth at both end faces of said tooth, the dimensions of said depression corresponding to the dimensions of said lobe on said cylindrical surface of said driving rotor so that during rotation of said driving and driven rotors, said lobe covers said depression and separates the zone of equalized pressure from the suction zone.

2. The rotary displacement machine according to claim 1 wherein the front side, in the direction of rotation of the driven rotor, of said depression on said cylindrical surface of said tooth of said driven rotor is described by an arc whose center lies on the pitch circle of said driven rotor and whose radius is equal to the difference between the radii of the pitch circle of said driven rotor and of the inside circle of said depression,

the front side, in the direction of rotation of said driving rotor, of said lobe is described by an arc whose center lies on the pitch circle of said driving rotor and whose radius is equal to the difference between the radii of the outside circle of said lobe and of the pitch circle of said driving rotor and wherein the back side of said lobe is described by a shortened epicycloid formed by the point of intersection of the inside diameter of said depression on said cylindrical surface of said tooth with said space between said teeth of said driven rotor when the pitch circle of said driven rotor rolls without slipping over the pitch circle of said driving rotor.

3. The rotary displacement machine according to claim 1 wherein the front side, in the direction of rotation of said driven rotor, of said depression on said cylindrical surface of said tooth of said driven rotor is described by an arc whose center lies outside the pitch circle of said driven rotor while the front side, in the direction of rotation of said driving rotor, of said lobe is described by a rolling curve which satisfies the requirement of continuous contact between said front side of said depression and said front side of said lobe and wherein the back side of said lobe is described by a shortened epicycloid which is formed by a point of intersection between the inside diameter of said depression on said cylindrical surface of said tooth with said space between said teeth of said driven rotor when the pitch circle of said driven rotor rolls without slipping over the pitch circle of said driving rotor. 

1. A rotary displacement machine comprising: a casing having an internal surface; a pipe connection located on said casing and serving for sucking in the working fluid; a pipe connection located on said casing and serving for discharging the working fluid; a straight-toothed driving rotor installed rotatably in said casing; said driving rotor having a cylindrical surface; lobes located on said cylindrical surface of said rotor, each lobe being positioned between said straight teeth of said rotor; a straight-toothed driven rotor installed inside said casing; a gear train consisting of two meshing gears for transmitting rotation from said driving rotor to said driven rotor and for ensuring a guaranteed clearance between said teeth of said driven and driving rotors; a shaft for said driving rotor which carries one of said meshing gears; a shaft for said driven rotor which carries the other of said meshing gears; an external cylindrical surface for each tooth of said driven rotor; spaces between said teeth of said driving rotor and driven rotor; a cavity for said driven rotor formed by said space between said teeth of said driven rotor and the internal surface of said casing; a cavity for said driving rotor formed by said space between said teeth of said driving rotor and the internal surface of said casing; a depression serving to equalize pressure between said cavity of said driven rotor and said cavity of said driving rotor during compression of the working medium, said depression being located on said cylindrical surface of each tooth of said driven rotor and limited by the body of said tooth at the front edge of said driven rotor tooth, in the direction of rotation of said driven rotor, and by the body of the same tooth at both end faces of said tooth, the dimensions of said depression corresponDing to the dimensions of said lobe on said cylindrical surface of said driving rotor so that during rotation of said driving and driven rotors, said lobe covers said depression and separates the zone of equalized pressure from the suction zone.
 2. The rotary displacement machine according to claim 1 wherein the front side, in the direction of rotation of the driven rotor, of said depression on said cylindrical surface of said tooth of said driven rotor is described by an arc whose center lies on the pitch circle of said driven rotor and whose radius is equal to the difference between the radii of the pitch circle of said driven rotor and of the inside circle of said depression, the front side, in the direction of rotation of said driving rotor, of said lobe is described by an arc whose center lies on the pitch circle of said driving rotor and whose radius is equal to the difference between the radii of the outside circle of said lobe and of the pitch circle of said driving rotor and wherein the back side of said lobe is described by a shortened epicycloid formed by the point of intersection of the inside diameter of said depression on said cylindrical surface of said tooth with said space between said teeth of said driven rotor when the pitch circle of said driven rotor rolls without slipping over the pitch circle of said driving rotor.
 3. The rotary displacement machine according to claim 1 wherein the front side, in the direction of rotation of said driven rotor, of said depression on said cylindrical surface of said tooth of said driven rotor is described by an arc whose center lies outside the pitch circle of said driven rotor while the front side, in the direction of rotation of said driving rotor, of said lobe is described by a rolling curve which satisfies the requirement of continuous contact between said front side of said depression and said front side of said lobe and wherein the back side of said lobe is described by a shortened epicycloid which is formed by a point of intersection between the inside diameter of said depression on said cylindrical surface of said tooth with said space between said teeth of said driven rotor when the pitch circle of said driven rotor rolls without slipping over the pitch circle of said driving rotor. 